(Reuters) -U.S. stock index futures slipped on Tuesday, pressured by a rise in longer-dated Treasury bond yields as President Donald Trump's decision to fire a Federal Reserve governor renewed concerns about the central bank's independence.

Investors also awaited Nvidia's results and a key inflation report later this week for more insight on artificial intelligence and interest rate cuts - the two big themes behind recent market gains.

The chip giant's shares were marginally higher in premarket trading.

In an unprecedented move, Trump said he was removing Governor Lisa Cook over alleged improprieties in obtaining mortgage loans, prompting investor unease about what it could also mean for the outlook on monetary policy just weeks ahead of the Fed's meeting.

Trump's action is likely to face legal challenges but, if successful, it would let him nominate a new member to the central bank's board at a time when he has called for lower interest rates.

"Trump already appointed a majority of Fed governors, without changing policy independence. If the dismissal survives the courts, the Senate must confirm any successor. Fed presidents still have policy votes. Faith in these checks may limit the negative market reaction," said Paul Donovan, chief economist at UBS Global Wealth Management.

Despite lingering inflation pressures, traders have been pricing in a 25-basis-point interest rate cut for September, encouraged by dovish signals from Fed Chair Jerome Powell, data pointing to labor market weakness and the likelihood that Trump nominee Stephen Miran could fill up a recent central bank vacancy.

However, key upcoming inflation and jobs reports could prompt investors to reassess rate-cut expectations.

At 05:41 a.m. ET, Dow E-minis were down 76 points, or 0.17%, S&P 500 E-minis were down 8 points, or 0.12%, and Nasdaq 100 E-minis were down 30.75 points, or 0.13%.

U.S. 10-year and 30-year Treasuries also fell and the dollar declined against major currency pairs. Bond yields move inversely to prices.

Nvidia's results on Wednesday will be a major catalyst for U.S. stocks that have rallied over the past few years on the potential earnings growth from artificial intelligence. Investors will also look for details on how the recent revenue-sharing deal with the U.S. government could impact forecasts.

The AI enthusiasm has also pushed up valuations of Wall Street's benchmark S&P 500 to above long-term averages, heightening the risk of a selloff in case the chip giant falls short of market expectations.

Interactive Brokers rose 4.3% as the trading platform is set to join the S&P 500 before markets open on August 28.

Wolfspeed gained 3% after the chipmaker surpassed quarterly revenue expectations.

Monthly reports on durable goods and the Conference Board's consumer confidence data are expected later in the day, along with remarks from Richmond Fed President Thomas Barkin.

On the trade front, Trump threatened countries that have digital taxes with "subsequent additional tariffs" if those nations do not remove such legislation, while India is expected to face duties starting on Wednesday.

(Reporting by Johann M Cherian in Bengaluru; Editing by Devika Syamnath)